Discharge lamp ballasting circuit



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His Acicgovneg United States Patent 3,233,148 DISCHARGE LAMP BALLASTNG ClRCUlT William H. Lake, Mayfield Heights, Qhio, assignor to General Electric Company, a corporation of New York Filed Apr. 25, 1961, Ser. No. 105,503 12 Claims. (Cl. 315-200) This invention relates to a new type of ballasting or current regulating circuit which uses a rectifier-capacitor bridge circuit for operating discharge lamps on rectified alternating current at high eiciency.

The conventional discharge lamp ballast utilizes an inductive device, that is a winding on a magnetic core. It is relatively etiicient but has the disadvantage of bulk and weight. Small size and light weight are naturally preferable. A miniature ballast is particularly desirable for applications where it would be mounted integrally with the lamp, as for instance a fluorescent panel lamp, to permit a lightweight economical fixture design. However the only practical lightweight ballasts available up to the present have utilized resistive devices and their inefficiency has rendered them unattractive. Furthermore, a resistive ballast entails a heat dissipation problem and is severely limited in regard to the lamp wattage or arc length which can be operated and regulated from the usual 1Z0-voit A.C. circuit.

The general object of the invention is to provide ballasts for electric discharge lamps which are lightweight and compact and comparable or superior in eiiiciency to conventional inductive ballasts.

A specic object of the invention is -to provide discharge lamp operating and ballasting circuits sufciently lightweight and compact to permit integral mounting with the lamp.

In accordance with the invention, I have developed a new type of ballast for electric discharge lamps which may be designated a rectifier-capacitor bridge ballast. The rectifier-capacitor bridge is similar in its wiring conliguration to the voltage doubler circuit heretofore used in electronic equipment as a low cost transformerless D.C. power supply providing a D.C. voltage at approximately twice the A.C. line voltage. However the rectifiercapacitor bridge used as a ballast for a discharge lamp according to the invention operates in radically different fashion from the conventional voltage doubler circuit wherein the desired output is a DJC. voltage with a minimum of pulsation or superimposed A.C. and efficiency is substantially immaterial. By contrast, in the rectiiiercapacitor bridge ballasting circuit, efliciency is a prime consideration and economics dictate that all components be operated at their maximum power capability. In the rectifier-capacitor bridge ballast, the lamp operates on unidirectional rectified current having a very high ripple factor. Current flow through the lamp results not only from the discharging but also from the charging of the capacitors of the bridge. The lamp current has a very pronounced alternating component having a fundamental frequency of twice the line frequency superimposed on the unidirectional component. In the mode of operation according to the invention, the energy stored in the capacitors of the bridge by the input voltage is transferred with high etiiciency to the lamp load. This mode of operation is made possible because the discharge lamp provides a load operable in two different impedance states with a voltage-sensitive transition point.

A feature of the mode of operation of the rectifiercapacitor ballast is that the voltage across the capacitors reverses cyclically in polarity at line frequency. This entails that A.C. type capacitors, that is non-polarized Patented Feb. l, 1966 ICC capacitors, must be used. At the same time however, the mode of operation according to the invention permits the use of much smaller capacitors for a given lamp load current than would otherwise be required.

For further objects and advantages and for a better understanding of the invention, attention is now directed to the following explanation of the principles and mode of operation of the ballasting circuit and to the description of various embodiments, taken in conjunction with the accompanying drawings. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings, wherein like reference numerals indicate elements performing corresponding functions in the several views:

FIG. 1 is a schematic diagram of the basic rectifier capacitor bridge ballasting circuit of the invention for operating a discharge lamp.

FIG. 2 illustrates the static volt-ampere characteristic of a self-sustaining gas discharge such as a discharge lamp.

FIGS. 3a, b and c are curves illustrating voltage and current relationships in a rectifier-capacitor bridge circuit for three different modes of operation, the last representing the preferred mode of operation according to the invention.

FIG. 4 is a curve showing power optimization in operation according to the preferred mode.

FIGS. 5a, b and c are schematic diagrams illustrating inductive modifications of the rectifier-capacitor bridge ballasting circuit.

FIG. 6 is a schematic diagram of a practical single lamp bridge ballasting and starting circuit.

FIG. 7 is a schematic diagram of a practical two-lamp circuit using two bridges in parallel.

FIG. 8 is a schematic diagram of a single lamp ballast-v BASIC CIRCUIT The basic rectifier-capacitor bridge circuit of the invention is shown in FIG. 1 formed of two branches each comprising a rectifier and a capacitor connected in series between input junction points, the rectiiiers being poled for conduction in opposite directions. The rectifiers are preferably high efficiency semi-conductive diodes such as silicon diodes, and the capacitors are of a type capable of withstanding A.C. As illustrated, the A.C. line voltage at terminals Sl, S2 is supplied to input junctions il, i2; one branch comprises diode D1 and capacitor C1 connected in series wherein D1 is poled to permit current iiow from junction il; the other branch comprises diode D2 and capacitor C2 wherein diode D2 is poled to permit current ow towards junction jl. The junction points of the diode and capacitor in each branch, namely i3 and f4, form the output points across which the utilization or load circuit is connected. The load circuit comprises the load proper P1 connected across load terminals S1, S2, and an inductor L1 connected in series therewith. The load proper P1 is a discharge device having a negative resistance characteristic such as a discharge lamp. The inductor serves to limit the rate of change of current through the lamp and is made necessary by the negative impedance characteristic of the lamp in its high conduction state. The value of L1 is a dominant factor in determining the mode of operation and performance of the circuit.

A convenient characteristic for dening performance in the rectifier-capacitor bridge circuit herein is the ripple factor Rf based on average current (rather than R.M.S.

current). lt may be defined as follows over an integration period T:

l T. IDC-TL #di The rectifier-capacitor bridge circuit limits the current through the discharge lamp according to the relationship where O=capacitance and d gg=rate of change of voltage across the capacitance If the lamp P1 is the only element in the load circuit and the peak D.C. voltage developed by the rectifiercapacitor bridge circuit is suiiicient to ignite the lamp, current will llow in bursts which are limited in magnitude only by the size of the capacitors and their internal dissipation characteristics. This mode of operation is not suitable for the common forms of discharge lamps such as fluorescent lamps-or mercury vapor lamps in which high peak currents are inecient in producing useful radiation. In order to overcome these dithculties, inductor L1 is placed in series with the lamp in order to broaden the current pulse. At the opposite extreme where the inductance of L1 is so great as to eliminate substantially any liuctuations in current through the lamp, the size of the capacitors C1, C2 which must be provided to achieve a given power input into the lamp, becomes inordinately large. With intermediate values of inductance for L, that is values less than that which will result in substantially steady direct current tiow through the lamp, the impedance or volt-ampere characteristic of the lamp becomes very important in determining the manner in which current is drawn from the bridge.

The static volt-ampere characteristic of a discharge lamp exhibits two discrete regions which are of particular interest in connection with the present circuit. ln FIG. 2, the curve illustrates a static volt-ampere characteristic typical of a self-sustaining gas discharge and is indicative of the characteristic of a fluorescent lamp. For very small values of discharge current, that is for values less than that at point a, the impedance characteristic is positive as shown by the upward slope of the volt-ampere curve. This region, which may be termed region l, is the classic glow discharge region comprising the normal cathode fall region followed by the abnormal cathode fall region, and is characterized by the production of electrons through secondary emission. At point a, whereof the corresponding voltage may be called the transistion voltage, thermionic emission becomes sufficiently large that the discharge current is no longer voltage limited and the full arc discharge ensues. The arc discharge region to the right of point a may be termed region Il. In it, the impedance characteristic is negative as indicated by the downward slope of the curve. lf the current is brought up to the value corresponding to point a, it will thereafter continue to increase except inasmuch as it is limited by the external circuit. in the normal alternating current operation of the common forms of discharge lamps such as the uorescent lamp, the volt-ampere characteristic is traversed once per half cycle; that is at each hair cycle of the applied line voltage, the lamp starts in a high impedance state, converts to a low impedance state, and reverts to a high impedance state. The transition voltage corresponding to the passage from high to low impedance state is dependent upon the emission characteristic or work function of the cathode, the current density, and the starting gas concentration.

MODES OF OPBRATON In the operation of a discharge lamp by a rectifier-capacitor bridge cir-cuit, l have determined that three characteristic modes of operation `are possible. For convenience, these three modes may be designated and defined as follows:

Mode A .-Operation in the low (region il) impedance portion of the volt-ampere characteristic of the lamp-substantially constant direct current.

Mode B.-Operation with transition from high (region I) to low (region Il) impedance portions of the volt-ampere characteristic and return once per cycle-unidirectional current with large line frequency component superimposed.

Mode C Operation with transition from high (region l) to the low (region ll) impedance portions of the voltampere characteristic and return twice per cycle-unidirectional current with a large AC. component at twice the line frequency.

Which of the three foregoing modes will occur in a given lamp-circuit combination is determined primarily by the value or' the series inductance in the load circuit. The series inductance reduces variations in load current, that is the AC. component, in proportion to its value. FGS. 3a, b and 'c illustrate the wave forms associated with the three different modes of operation A, B and C. The curves are labelled and show on the same ordinate scale in each case the voitage VCI across capacitor Ci, the voltage V02 across capacitor C2, and the voltage V s which is the sum of the voltages across the capacitors and which is applied to the utilization circuit consisting of L1 and Pil in series. The current IP flowing through the lamp is shown on different scale. The time base is the same in all; it will be appreciated that one cycle at a frequency of 60 c.p.s. is 16.7 milliseconds. The curves represent actual measurements and wave forms obtained through the use of a cathode ray oscilloscope using for the lamp a T12 (l1/2" nominal diameter) liuorescent lamp of 62.5 arc length provided with a starting gas filling consisting of argon at a pressure of 3 millimeters of mercury. The pertinent conditions are stated in the legend appended to each iigure.

MODE A When the series inductance is large, greater than `about 0.5 henry for the stated lamp, operation in mode A occurs; that is the lamp remains at all times in the low impedance negative portion (region Il) of its volt-ampere characteristic. Current and voltage wave forms are illustrated in FIG. 3a. The impedance of the load circuit is dominated by the inductance which maintains the load current relatively constant, as indicated by lp. The substantially constant load current causes the capacitors to discharge at a substantially constant rate as evidenced by the straight line downward sloping portions m curves Vgl and VGZ in-between the sinusoidal charging intervals. ln this case7 the operating current level is fixed by the size of the capacitors C1 and C2 and by the voltage drop across the lamp. The slope of the discharge characteristic dv/dl is a direct function of arc length in the case of discharge lamps of the same diameter and otherwise similar in characteristics.

MODE B Reduction or the inductance value of L1 to less than 0.5 henry permits the variation in current to increase, that is a larger superimposed A.C. component to flow, and the change in lamp impedance during a cycle becomes an important factor in determining the voltage and current wave forms. Wave forms are illustrated in FlG. 3b. During a cycle of the applied line voltage, current through the lamp increases and the lamp impedance converts from high to low. The capacitors are capable oi supplying only voltage can be reduced to a certain extent by design of the lamp. Of course reduction of the series inductance has practical limits because it causes increased peaking of the current. High peak currents are to be avoided, particularly with low pressure discharge lamps, because the efficiency of light production decreases and the life of the lamp cathode may be adversely affected.

The losses in the rectifier-capacitor bridge ballast may be divided into rectifier losses, capacitor losses, and inductor losses. The losses in the rectifiers occur chiefly during forward conduction when a small voltage drop appears across the junction. With highly efficient silicon diodes, such losses are relatively low; by way of example, in a rectifier-capacitor ballast providing 600 milliamperes to a 70-watt fiuorescent lamp, the rectifier losses are approximately watt. The capacitor losses depend upon the dissipation factors of the capacitors. Paper capacitors may for instance have 0.5% dissipation factors and electrolytic type capacitors may have 3% dissipation factors. For the same example, the capacitor losses are 3A watt using 0.5% dissipation factor capacitors, and 4 watts using 3% dissipation factor capacitors. The inductor losses are due to the usual copper losses to the core and iron core excitation losses. With a fair compromise on wire size and core size, inductor losses are less than 1 Watt for the same example.

An advantage of the mode C operation of the rectifiercapacitor bridge ballast in accordance with the invention is a higher input power factor than with conventional capacitive circuits. Normally a voltage doubler circuit operates with a leading power factor below 30%. The rectifier-capacitor bridge ballast of the invention permits approximately half the input current to be drawn While the input voltage has the same polarity and this results in a power factor of approximately 50%.

INDUCTIVE CIRCUIT MODIFICATIONS There are several modifications of the basic rectifiercapacitor bridge ballast circuit which can extend the range of applicability of the circuit by the addition of inductance in the input circuit. The bridge proper, consisting of D1 and C1 in the one branch and D2 and C2 in the other branch may conveniently be regarded as the input circuit; the utilization circuit consisting of inductor L1, lamp P1, plus capacitors C1 and C2 may be regarded as the output circuit. The cardinal feature of these modifications consists in the presence of inductance in the input circuit causing additional voltage to be stored in the capacitors so that the dynamic transformation ratio is increased. This increased voltage is in some respects similar to an increase in the input line voltage with this difference that the increment in voltage added in this fashion by inductance is obtained by peaking the input wave form.

FIGS. 5a, b and c illustrate three different specific circuits which add inductance in the input circuit. In the circuit of FIG. 5a, which is otherwise similar to FIG. l, an inductor L2 is placed in series with the input bridge circuit, that is between line terminal S1 and junction jl of the bridge. In FIG. 5b, inductance is likewise added in the input circuit but is split into two portions, one inductor L3 being placed in one branch of the bridge between terminal jl and diode DI, and the other inductor L4 being placed in the other :branch between terminal jl and diode D2. If desired, magnetic coupling may be provided between inductances L3 and L4. In FIG. 5c, the added inductance is effectively in both t'ne input and output circuits of the bridge and is again split into two portions. One inductor LS is inserted between junction point jZ and capacitor C1 and another inductor L6 is inserted between junction i2 and capacitor C2. Here again magnetic coupling between inductances L5 and L6 may be provided if desired. Since L5 and L6 are in both the input and output circuits, interaction between the lamp load current and the capacitor charging currents requires a larger value of inductance for the same power output than is necessary with the other circuits. However with the -circuit of FIG. 5c since the voltage peaking which occurs at the maximum of the input line voltage wave form is applied directly to the load, smoother load current wave form results and higher lamp efficiency may be achieved.

Essentially, the circuits of FIG. 5a, b and c substitute inductive energy storage in part for capacitive energy storage. The energy stored in the inductors is in proportion to the square of the current, being based on the relationship LIZ. In view of this relationship, it is evident that the addition of inductance in the input circuit is more effective with circuits intended to provide high lamp operating currents than low currents. The inductive modification may be used where the transitional voltage of the lamp is too high to permit mode C operation from the simple rectifier-capacitance bridge circuit at the available line voltage. By resorting to the inductive modification, a longer length of fluorescent lamp, that is a larger size of lamp, may be operated from the same line voltage. Alternatively, the size of the capacitors CI, yC221 may be reduced for a given size of lamp and then the choice of circuit configuration becomes largely a matter of economics, that is the governing consideration becomes the saving in cost of capacitors offset by the additional cost of inductors in the primary circuit. In general, the stored energy utilization of the circuit with the inductive modification is somewhat poorer because circuit losses are generally higher with inductive magnetic components than with capacitive components.

PRACTICAL BALLASTING CIRCUITS In a practical rectifier-capacitor bridge ballast circuit, provision must be made for preheating the cathode at the negative end of the lamp. Since the current, even though pulsating, is unidirectional, it is not necessary or ordinarily desirable to preheat the electrode at the other end which operates as anode. In fact, in fluorescent lamps specifically designed for operation in a rectifier-capacitor ballast circuit, a cathode may be provided at one end only and the other end may use simply a metal plate or other suitable structure to serve as anode. In addition, in all but the shortest or smallest sizes of lamps having low striking potentials, where operation is to be had from the usual volt A.C. distribution lines, some means must be provided to initially ignite or strike the lamps. A practical rectifier-capacitor bridge circuit meeting these requirements is illustrated in FIG. 6.

Referring to FIG. 6, the circuit combination includes the receier-capacitor bridge circuit configuration previously described with reference to FIG. 1. In addition, a transformer 10 is provided having a primary winding 11, a low voltage center-tapped secondary winding I2, and a relatively high voltage, low current auxiliary winding 13. Primary winding il is connected across the line or switch terminals S1, S2, terminal S2 being the low or grounded side of the A.C. supply. Secondary winding 12 is connected to supply preheating current to cathode 14 at the negative end of the lamp and has a connection from its center tap to terminal j4 of the bridge. The lamp P1 is shown with a simple anode plate 1S at its other end; the anode may also be a filamentary structure similar to the cathode but there is no need to heat it. Auxiliary winding 13 extends from the high (ungrounded) side of the primary winding and is connected to a capacitiv'e starting means such as a conductive strip or coating on the lamp envelope, or a metal member le which extends the length of the lamp and may be built into (but insulated from) the fixture channel. Since auxiliary winding 13 supplies only a very low capacitive current to sesame a limited amount of charge with the result that the instantaneous current through the lamp falls to a low value and the lamp reverts to the high impedance portion of its volt-ampere characteristic for the remainder of the cycle. A full cycle of operation is required before the Voltage on the capacitors can build back up to the transition voltage level of the lamp. The result is that current through the lamp flows heavily for approximately a halfcycle of each full cycle (referred to the line frequency) and is practically extinguished during the succeeding halfcycle. This causes a very pronounced flicker in the light output of the lamp and is an unsatisfactory mode of operation.

Mode C Further reduction of the value of series inductance L1, to less than 0.1 henry for the suibject lamp, further shortens the current pulses and causes the timing to change such that the capacitors charge and discharge alternately instead of simultaneously. Wave forms are illustrated in FIG. 3c. The lamp impedance passes from high to low and reverts to high during each half-cycle. The transition voltage is reached twice per cycle referred to the line tfrequency, instead of only once as in the mode B operation. The current through the lamp has a unidirectional component and a large A.C. component superimposed thereon; however the fundamental `frequency ort the A.C. component is twice the line frequency. As a result, ilicker from the lamp occurs at twice the line frequency and is reduced to an insignificant level, so that efficient operation results. The ripple factor Rf according to the definition previously 'given is in excess of 75%; it is preferably in the range of y85% to 115%, a typical value being 100%. vThis mode of operation maybe described as lbimodal with transitions at twice the -line irequency. It is the desired mode of operation in accordance with the invention and results in efticient operation of the lamp, sulbstantially ickerless light output, and maximum utilization of the capacitors in the rectifiercapacitor bridge.

POWERS OPTIMIZATION From the point of View of maximum power utilization, a rectiiier-capacitor bridge ballasting circuit prol viding lamp operation with a lbimodal impedance characeteristic alternating at twice the line frequency achieves a unique and unexpectedly advantageous situation. In conventional usage, the maximum power drawn trom a voltage doubler circuit cannot exceed approximately 50% olf the power stored in `the capacitors and is generally much less. This is a natural consequence of impendance matching. However operation according to the invention in mode C results in the discharge of one capacitor fbeing held off until the other capacitor is at or near its peak charge. Thus the voltage during discharge is maximized and the power derived from the circuit approaches the total energy ilowing into the capacitors per cycle. The low .pressure discharge lamp such as the uorescent lamp ideally mee-ts the Icircuit requirements ttor this type of operation inasmuch as it is a dual impedance device which is triggered yfrom a high impedance state to a low impedance state when the applied voltage reaches a predetermined peak, and which reverts to the high impedance state when the discharge current drops below a certain minimum.

The manner in which the power supplied to the lamp is optimized in mode C operation according to the invention, by comparison with operation in modes A or B, is illustrated by the curve of FIG. 4. In mode A operation wherein the impedance of the lamp is at all times in the low negative resistance portion orf the volt-ampere characteristics, the -relative power is arbitrarily taken as unity. In mode B wherein Vthe lamp operates with a ibimodal impedance characteristic alternating at the line frequency,

S the relative power averages about 1.2. In mode C wherein the lamp operates with a bimodal impedance characeteristic alternating yat twice the line frequency, the relative power climbs in excess of 1.86. Thus mode C operation in accordance with the invention provides an increase or" in the effective utilization of the capacitors of the bridge circuit in terms of the power supplied to the lamp. Otherwise stated, by resorting to mode C operation, the size of capacitors required in the rectifiercapacitor bridge circuit to supply rated power to a given lamp drops at most to hall the size which would be required with mode A operation. Since the capacitors are the major cost element in the circuit, this result is economically very signiiicant.

BASIC CIRCUIT CHARACTERISTICS The reactance of inductor L1 is of primary importance in determining the mode of operation. It is the energy stored in the inductance during the current pulse which determines the maintaining ycurrent through the lamp when the voltage across the capacitors is very low. ln a given circuit coniiguration, in order to increase the maximum arc length, that is in order to operate longer iluorescent lamps, the inductance of L1 must Ibe reduced or the input voltage must be increased. Of course there are practical limits to the extent to which L1 may be decreased inasmuch as reduction of L1 entails more peaked current pulses with resultant lowered eiciency.

In a given .circuit coniiguration, the power supplied to the `lamp is directly proportional to the capacitance of Cl and CZ. A natural consequence of the alternating dischange of the capacitors is a limit on the degree of unbalance which may be tolerated before visible dicker appears. When capacitors C1 and C2 are unequal in value, a line frequency component is introduced into the load current which tends to produce flicker. In general, a difference of 20% in the capacitance of the two branches of the tbridge produces [barely discernible dicker in the `light output of the lamp, so that the unb-alance should be limited to 20%.

Inasmuch as the energy stored in a capacitor varies as the square of the voltage to which it is charged, it might be expected that the power supplied tothe lamp by the rectifier-capacitor bridge would vary as the square of the line voltage applied to the circuit. In fact, however, such is not the case; the power supplied to the lamp does increase with input voltage but increases approximately in direct proportion to the voltage tfor a stable operating point in the mode C region of operation. The explanation for this fact is that with higher applied voltage, the transition point lbetween high and low impedance states in the volt-ampere characteristic of the lamp occurs earlier in the cycle and causes a compensa-ting reduction in the power transferred to the lamp. Due to conversion eiiiciency variations inherent in the lamp, the light output shows 'considerably less variation than the input power or wattage to the lamp for the sa-me Variation in line voltage.

In a given circuit configuration, the power delivered to the lamp is a direct function of the arc length. For lamps of the same type such as for instance low pressure iluorescent lamps of one and one-half inch nominal diameter (T12), the power delivered to the lamp will increase in proportion to the length of the lamp. For the usual one and one-half inch diameter fluorescent lamp, power delivered to the lamp increases at the rate of approximately 0.9 watt per inch of lamp for ripple ffactor operation in mode C. As the arc length is increased, the transition voltage also increases and therefore occurs later in the cycle. Eventually a point is reached where the operating mode is unstable and may shift from mode C to mode B, and the power supplied to the lamp decreases. Decreasing the size of the inductance L1 extends the range of impedance variation which can be accommodated by the circuit. Also the transition 9 member 16, it may be made of very tine wire in order to keep the cost down. A relatively high resistance i7 is serially inserted between winding i3 and member 16 in order to avoid excessive current flow in the event of accidental short-circuiting of member to ground.

In operation of the circuit of FIG. 6, capacitors C1, C2 initially charge to twice the peak A.C. line voltage and in addition alternating voltage is applied to capacitive starting aid member 16. Preheating current is simultaneously applied across cathode 14 and as thermionic emission begins, current starts to iiow, the lamp ionizes and ignites. Operation thereafter proceeds in the manner previously described, that is, the lamp operates with a bimodal impedance characteristic alternating at twice the line frequency.

Where it is desired to operate two lamps, each may be provided with its rectifier-capacitor bridge and some economies may be effected by utilizing a single transformer with an additional electrode heating winding for the second lamp. Such an arrangement is illustrated in FIG. 7 wherein one lamp Pil is operated by bridge Bl and a second lamp P2 is operated by bridge B2, both bridges being energized in parallel from line terminals Sl, S2. ln generally similar fashion to the contiguration of FIG. 6, transformer 10 has a primary winding 11 connected across the line terminals, secondary windings i2 and 18 which supply cathode heating current to lamps P1 and P2 respectively, and a single auxiliary or extended winding i3 which supplies voltage to a single capacitive member- 16 suhicing for both lamps.

The circuit of FiG. 8 utilizes a different arrangement to assure starting of a longer arc length lamp, which may be referred to as a four-diode boosting circuit. in this arrangement, the starting aid or capactive member may be dispensed with and the four-diode bridge boosts the voltage applied across the lamp terminals sufficiently to cause it to start. As illustrated, a four-element rectiiier bridge comprising diodes 2@ to 23 is inserted in the load circuit of the rectifier-capacitor bridge between inductor Ll and lamp Pl; the diodes are poled for conduction from junction point i5 to junction point i6, thereby permitting normal current tiow in the load circuit. The auxiliary high voltage winding 13 of transformer 1t) is connected across the conjugate joints j7, jfl of the tourdiode bridge. At starting, the D.C. voltage generated by rectication in the four-diode bridge is added serially to that provided by the rectifier-capacitor bridge and increases the total voltage applied across the electrodes of the lamp to the point where the lamp starts. After the lamp has entered into normal operation, diodes 2t), 2l and 22, 23 provide a pair of parallel paths through which the load current hows. Winding 13 of transformer 10 in this arrangement is a high reactance winding in order to avoid incurring excessive losses during normal operation. Alternatively winding i3 may be designed such that through the four-diode bridge it supplies part of the voltage and wattage to the lamps after starting and during normal operation.

By way of example of the invention, a circuit actually constructed and tested following the configuration of FiG. 6, operated a 72 long, 85 watt ftuoresc'ent lamp commonly designated 72T12/HO on a line supply voltage of 120 volts, 60 cycles A.C. The following values of circuit elements were used: for Ll, 0.07 henry; for C1 and C2, 20 microfarads each. Secondary winding 13 of transformer it) provided 220 volts KMS. measured from ground to the capacitive member 16. The circuit operated the lamp at rating without noticeable dicker. The total power consumed from the line was 90 watts and the ballast loss was 5 watts. The ballast eticiency was about 95% and the overall emciency of the system was 64.5 lumens per watt input from the line terminals, an eiciency better than that obtainable with the usual inductive ballast.

While specific embodiments of the invention have been l0 illustrated and described in detail, they are intended as illustrative and not in order to limit the invention thereto. Modifications will readily occur to those skilled in the art and it is intended by the appended claims to cover any such as fall within the true spirit and scope of the invention.

What l claim as new and desire to secure by Letters Patent of the United States is:

1. An operating and ballasting circuit for an electric discharge device comprising a rectifier-capacitor bridge having a pair of branches each including a rectier and a capacitor connected in series between alternating current input terminals, the rectiliers being poled for conduction in Aopposite directions in the two branches, and a utilization circuit means including an electric discharge device having a negative impedance characteristic connected across the junction points of the rectifier and capacitor in each branch, said utilization circuit means having an impedance proportioned to achieve substantial transfer of energy to said discharge device through the charging of said capacitors as well as through the discharging thereof.

2. An operating and ballasting circuit for an electric discharge device comprising a rectifier-capacitor bridge having a pair of branches each including a rectifier and a capacitor connected in series between alternating current input terminals, the rectiiers being poled for conduction in opposite directions in the two branches and the capacitors being substantially equal in value in both branches, and a utilization circuit means including an electric discharge device having a negative impedance characteristic connected across the junction points of the rectifier and capacitor in each branch, said utilization circuit means having an impedance proportional to achieve substantial transfer of energy to said discharge device through the charging of said capacitor as well as through the discharging thereof.

3. An operating and ballasting circuit for an electr-ic discharge device comprising a rectifier-capacitor bridge having a pair o branches connected between input terminals adapted for alternating current energization, each branch including a rectifier and a capacitor connected in series, the rectiiiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being connected to the other input terminal, and a utilization circuit means including an electric discharge device having a negative impedance characteristic connected across the junction points of the rectifier and capacitor in each branch, said utilization circuit means having a total impedance dominated by that of said discharge device operating in a bimodal mode at twice the frequency of the alternating current whereby to obtain through said device a current having a ripple factor in excess of 4. An operating and ballasting circuit for an electric discharge device comprising a rectier-capacitor bridge having a pair of branches each including a rectifier and a capacitor connected in series between alternating current input terminals, the rectiiiers being poled for conduction in opposite directions in the two barnches, and a utilization circuit including a series inductance and terminals for accommodating an electric discharge device load having a negative impedance characteristic connected across the junction points of the rectifier and capacitor in each branch, said inductance being proportioned, relative to the total impedance of said utilization circuit, to achieve operation of said discharge device with a bimodal impedance variation occurring at twice the frequency of the alternating current.

5. An operating and ballasting circuit for an electric discharge device comprising a rectifier-capacitor bridge having a pair of branches each including a rectier and a capacitor connected in series between alternating current input terminals, the rectiers being poled for conduction in opposite direction in the two branches and the capacitors being substantially equal in value in both branches,

and a utilization circuit including a series inductance and terminals for accommodating an electric discharge device load having a negative impedance characteristicconnected across the junction points of the rectifier and capacitor in each branch, said inductance being proportioned, relative to the total impedance of said utilization circuit, to achieve operation of said discharge device with a bimodal impedance varation occurring at twice the frequency of the alternating current.

6. An operating and ballasting circuit for an electric discharge device comprising a rectifier-capacitor bridge having a pair of branches connected between input ter- -minals adapted for alternating current energization at a predetermined voltage and frequency, each branch including a rectifier and a capacitor connected in series, both rectifiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being substantially equal in value and connected to the other input terminal, and a utilization circuit means including an electric discharge device having a negative impedance characteristic connected across the junction points of the rectifier and capacitor in each branch, said utilization circuit means having an impedance proportioned in respect of the alternating current input voltage and frequency and the values of said capacitors to achieve in said discharge device a bimodal impedance characteristic with a cycle of transitions occurring at twice said predetermined frequency.

7. An operating and ballasting circuit for an electric discharge device comprising a rectifier-capacitor bridge having a pair of branches connected between input terminals adapted for energization by an alternating current input at a predetermined voltage and frequency, each branch including a rectifier and a capacitor connected in series, the rectitiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being substantially equal in value and connected to the other input terminal, and a utilization circuit including a series inductance and an electric discharge device having a negative impedance characteristic connected between the junction points of the rectifier and capacitor in each branch, said series inductance being proportioned such that said utilization circuit has a total impedance dominated by that of said discharge device operating in a bimodal rnode at twice said predetermined frequency whereby to obtain through said discharge device a current having a unidirectional component with an alternating component superimposed thereon having a fundamental frequency of twice said predetermined frequency and having a ripple factor in excess of 75%.

8. A11 operating and ballasting circuit for an electric disc-barge device comprising a rectifier-capacitor bridge having a pair of branches connected between input terminals for alternating current energization, each branch including a rectifier and a capaci-tor connected in series, the rectifiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being connected to the other input terminal, said branches forming an inp-ut circuit, inductance serially included within said input circuit for increasing the energy transfer into said capacitors, and a utilization circuit means including an electric discharge device having a negative impedance characteristic connected across the junction points of the rectifier and capacitor in each branch, said utilization circuit means having a total impedance proportioned to achieve substantial transfer of energy to said discharge device during the charging periods of said capacitors as well as during the discharging periods.

9. An operating and ballasting circuit for an electric discharge device comprising a rectifier-capacitor bridge having a pair of branches connected between input terminals for alternating current energization at a predetermined voltage and frequency, each branch including a rectifierand a capacitor connected in series, the rectiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being substantially equal in value and connected to the other input terminal, said branches forming an input circuit, inductance serially included within said input circuit for increasing the energy transfer into said capacitors, a utilization circuit including an electric discharge device having a negative impedance characteristic connected between Ithe junction points of the rectifier `and capacitor in each branch, and inductance serially included within said utilization circuit for increasing the duration of conduction through said device, said utilization circuit having a total impedance dominated by that of said device operating in a bimodal-mode a-t twice said predetermined frequency.

Iii. A starting and operating circuit for an electric discharge device comprising a pair of input terminals for alternating current energization, a rectier-capacitor bridge having a pair of branches connected across said input terminals, each branch including a rectifier and a capacitor connected in series, the rectiiiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being substantially equal in value and connected to the other input terminal, the junction points of the rectifier and capacitor in each branch forming output junctions, a utilization circuit including series inductance and terminals to accommodate an electric discharge device connected across said output junctions, said utilization circuit having an impedance proportioned to achieve substantial transfer of energy to said discharge device during the charging periods of said capacitors as well as during the discharging periods, a transformer having a primary Winding connected across said input terminals, a secondary winding in said transformer having terminals for connecting to one electrode of said device operating as cathode and supplying preheating current thereto, and an auxiliary high-voltage, low current capacity Winding in said transformer having a terminal for connection to a conductive member in capacitive relationship to said device in order to supply an alternating voltage thereto whereby to ignite said device.

11. A starting and operating circuit for a pair of electric discharge devices each including a pair of electrodes comprising a pair of input terminals adapted for alternating current energization, a pair of rectifier-capacitor bridges each having a pair of branches connected across said input terminals, each branch including a rectifier and a capacitor connected in series, the rectifiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being substantially equal in value and connected to the other input terminal, the junction points of the rectifier and capacitor in each branch forming output junctions for each bridge, a pair of utilization circuits each including series inductance and one of said electric discharge devices connected across the output junctions of each bridge, said utilization circuits having impedances proportioned to achieve substantial transfer of energy to said discharge devices during the charging periods of said capacitors as well as during the discharging periods, a transformer having a primary winding connected across said input terminals, a pair of secondary windings in said transformer each connected to the electrode of one of said devices operating as cathode and supplying preheating current thereto, and an auxiliary high-voltage, low current capacity winding in said transformer, a conductive member in capacitive relationship to said devices, and a connection from said auxiliary winding to said conductive member to supply an alternating voltage thereto whereby to ignite said devices.

12. A starting and operating circuit for an electric discharge device comprising a pair of input terminals adapted for alternating current energization, a rectier-capacitor bridge having a pair of branches connected across said input terminals, each branch including a rectifier and a capacitor connected in series, the rectiiers being connected to one input terminal and poled for conduction in opposite directions, the capacitors being substantially equal in value and connected to the other input terminal, the junction points of the rectifier and capacitor in each branch forming output junctions, a utilization circuit including inductance, a `four-diode bridge and an electric discharge device connected in series across said output junctions, said rutilization circuit having an irnpedance proportioned to achieve substantial transfer of energy to said discharge device during the charging periods of said capacitors as Well as during the discharging 10 periods, a transformer having a primary winding connected across said input terminals and a secondary winding, said four-diode bridge having a pair of output terminals connected into said utilization circuit and a pair of input terminals connected to said secondary Winding whereby to boost the voltage applied across said discharge device at starting.

References Cited by the Examiner UNITED STATES PATENTS 2,668,259 2/1'954 stutsman 315-205 X 2,827,595 3/1958 Brurna et al. 315-243 X 3,031,599 4/1962 Paschke et a1 315-201 FOREIGN PATENTS 1,000,112 1/1957 Germany.

OTHER REFERENCES Analysis of the Voltaige-Tripling and Quadrupling Rectifier Circuits (by D. L. Waidelich and H. A. K. Taskin), Reprinted from Proceedings of the LRE., vol. 33, No. 7, July 1945.

5 JOHN w. HUCKERT, Primary Examiner.

DAVID J. GALVIN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,233,148 l February l, 1966 William H. Lake It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line l0, after "lamp", the hyphen should be a dash; line 14 after "cycle" the hyphen should be a dash; same column 4, line I9, after "cycle" the hyphen should be a dash; column 5, line I4, for "Mode C", in italics, read MODE C line 42, for "POWERS" read POWER column 5, lines 72 and 73, for "characteristics" read characteristic column 9, line 44, for "joints" read points column l0, line 33, for "proportional" read proportioned line 3S, for "capacitor" read capacitors same column l0, line 59, for "barnches" read branches Column l2, line 33, for "connecting" read connection Signed and sealed this 18th day of October 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. AN OPERATING AND BALLASTING CIRCUIT FOR AN ELECTRIC DISCHARGE DEVICE COMPRISING A RECTIFIER-CAPACITOR BRIDGE HAVING A PAIR OF BRANCHES EACH INCLUDING A RECTIFIER AND A CAPACITOR CONNECTED IN SERIES BETWEEN ALTERNATING CURRENT INPUT TERMINALS, THE RECTIFIERS BEING POLED FOR CONDUCTION IN OPPOSITE DIRECTIONS IN THE TWO BRANCHES, AND A UTILIZATION CIRCUIT MEANS INCLUDING AN ELECTRIC DISCHARGE DEVICE HAVING A NEGATIVE IMPEDANCE CHARACTERISTIC CONNECTED ACROSS THE JUNCTION POINTS OF THE RECTIFIER AND CAPACITOR IN EACH BRANCH, SAID UTILIZATION CIRCUIT MEANS HAVING AN IMPEDANCE PROPORTIONED TO ACHIEVE SUBSTANTIAL TRANSFER OF ENERGY TO SAID DISCHARGE DEVICE THROUGH THE CHARGING OF SAID CAPACITORS AS WELL AS THROUGH THE DISCHARGING THEREOF. 